1. Field of the Invention
The invention relates in general to a light tube driving device, and more particularly to a transformer of a light tube driving device.
2. Description of the Related Art
With the popularity of multi-media products, the application of liquid crystal display (LCD) in computer and TV is also becoming more and more popular. Generally speaking, the liquid crystal display uses a compact and high-efficient discharging light tube as the light source of a backlight module, and features thin thickness, high resolution and steady display quality.
The backlight module of a liquid crystal display is mainly composed of a discharging light tube such as a cold cathode fluorescent lamp (CCFL) and a transformer used for driving the cold cathode fluorescent lamp. Referring to FIG. 1, an exploded diagram of a conventional transformer is shown. The transformer 10 has a bobbin 11, a first core 13, a second core 15, a primary coil set 17 and a secondary coil set 19. After the transformer 10 is supplied with an electric current, a magnetic flux flows from a first end 15a of the second core 15 to a second end 15b, and flows through the first core 13 and returns to the second core 15.
However, since the voltage difference between the primary coil set and the secondary coil set is large, spark would easily occur between the coil on the primary coil set and the coil on the secondary coil set. Moreover, the stray capacitance effect easily occurs between the housing of the cold cathode fluorescent lamp and housing of the liquid crystal display. The stray capacitance effect will cause different CCFLs of an LCD to have different currents, hence affecting the stability of currents. When the currents flowing through a CCFL differs from one another, different CCFLs would have different luminance levels. Consequently, the luminance of the backlight module is non-uniformed. Moreover, a CCFL with higher luminance will have shorter lifespan. In order to achieve the stability of currents, a high voltage capacitor is disposed between each of the CCFLs and the secondary coil to reduce stray capacitance effect, such that the current difference between different CCFLs is reduced. However, the use of several high voltage capacitors is costive.